1. Field of the Invention
The invention relates to a process for the preparation of aryl sulfides by heating an iodoaromatic compound in the presence of elemental sulfur.
2. Discussion of the Background
Aryl sulfides are useful as industrial chemicals, such as mothproofing agents, herbicides, lubricants, antioxidants, organic semiconductors, plasticizers, high boiling point solvents, etc. Additionally, they are useful as intermediates for the preparation of insecticides and pharmaceuticals. Aryl sulfides generally have a wide fluid range having a low melting point and a relatively high boiling point. This behavior makes these compounds particularly suitable for use as heat transfer media and as mineral oil additives. A relatively simple, economic process for the preparation of these aryl sulfides is therefore of continued economic and industrial significance.
Several methods for preparing aryl sulfides are known. Typically, aryl sulfides such as phenyl sulfide have been prepared by the reaction of aryl halides with metal sulfides in polar solvents, often with copper salts as catalysts. U.S. Pat. Nos. 3,322,834 and 3,397,244 disclose methods of preparing aryl sulfides by heating aryl halides with an alkali metal sulfide and an alkali metal bisulfide, respectively. Alternatively, aryl sulfides can be prepared by reacting aromatic compounds with a sulfur chloride (U.S. Pat. No. 3,706,805) or by reacting a chloro- or bromo-aromatic compound with hydrogen sulfide at elevated temperatures (U.S. Pat. No. 4,010,210). A method is also known in which a naphthol and hydrogen sulfide are reacted to produce thionaphthols and naphthyl sulfides (U.S. Pat. No. 2,903,484). Aryl sulfides have also been produced by a disproportionation reaction by heating unsymmetrical aromatic sulfides at elevated temperatures (U.S. Pat. No. 4,044,056) and by heating aromatic thiols at high temperatures in the presence of an inert gas (U.S. Pat. No. 4,035,424).
A relatively simple procedure for preparing aryl sulfides is to heat an aryl chloride in the presence of elemental sulfur. The reaction of aryl chlorides with sulfur is disclosed by M. Schmidt (Inorg. Macromol. Rev. 1 (1970) 101). However, this reaction yields a complex mixture of products, which are mostly polymeric.
A need exists, therefore, for a simple industrial process for preparing aryl sulfides which is economical, efficient, and which produces high yields. Additionally, a simple high yield process which does not involve tedious workup procedures is preferred.